Arc welded joint between a carrier and a component rigidly connected to it

ABSTRACT

Arc welded joint between a carrier such as aluminium sheet as one electrode and as the other electrode a metal component with a continuous recess into which a stud-like weld-in part is introduced, wherein the weld-in part consists of a shank and a head which is enlarged in relation to the shank diameter via a step, penetrates into the recess in the component resting on the carrier and can be pressed into the pool of melt formed on the carrier so that the pool of melt adjacent to the wall of the recess embraces the outer rim of the head and the step, the pool of melt directly connecting the component, at least in the region of the edge of the wall of the recess facing the carrier, directly to the adjacent carrier. The outer rim of the weld-in part may protrude slightly beyond the component and penetrate into the recess with a projection or step such that, remote from the carrier, it can be pressed into the pool of melt to cover the entire wall of the recess including its two edges to its outer rim as well as the carrier and the head. The rim of the head may be designed as a radial melting edge which is located completely within the recess of the component and has a substantially blade-like cross section.

This is a continuation of application(s) Ser. No. 07/923,393, filed onJul. 31, 1992, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to an arc welded joint between a carrier as oneelectrode and a metal component with a continuous recess into which astud-like weld-in part is introduced as the other electrode, which isrigidly connected to the carrier and the component by arc welding.

A welded joint of this type is known from DE-AS 1 565 563. With thiswelded joint a shell-type metal sheet is arranged on a steel carrier,fox which purpose the shell-type metal sheet is pressed against thesteel carrier by means of a steel plate welded on the steel carrier. Theweld between the steel plate and the steel carrier is produced by meansof a stud which passes through the steel plate and is also guidedthrough a hole in the shell-type metal sheet. The stud is welded to thesteel carrier by arc butt welding, a continuous weld being producedbetween the steel carrier, the stud and the steel plate. This weld isnot impaired by the shell-type metal sheet because its hole issufficiently large for its rims still to be at a considerable distancefrom the weld. Furthermore, the shell-type metal sheet should not beincluded in the weld because it is usually provided with acorrosion-preventing coating, for example zinc coating or plasticsmaterial. These coatings, in particular zinc, would evaporate during thewelding process. The vapour penetrating the weld impairs the alloyforming the welding pool. Furthermore, the shell-type metal sheetcomplicates the welding process as it necessarily produces a distancebetween the steel carrier and the steel plate which then has to bebridged over by the pool of melt and the weld produced from it.

One object of the present invention is to design the bond produced bythe weld between a carrier, a metal component and a stud-like weld-inpart particularly thoroughly and therefore with comparatively highstrength.

BRIEF DESCRIPTION OF THE INVENTION

According to the present invention, we provide an arc-welded jointbetween a carrier as one electrode and a metal component with acontinuous recess into which a stud-like weld-in part is introduced asthe other electrode which is rigidly connected to the carrier and thecomponent by arc welding wherein the weld-in part consists of a shankand a head which is enlarged in relation to the shank diameter via astep, penetrates into the recess in the component resting on the carrierand, owing to the formation of a pool of melt on the carrier, can bepressed into this pool of melt such that the pool of melt adjacent tothe wall of the recess embraces the outer rim of the head and the step,the pool of melt directly connecting the component, at least in theregion of the edge of the wall of the recess facing the carrier,directly to the adjacent carrier.

Owing to the construction of the weld-in part from a shank having a headwhich is enlarged in relation to it and owing to the use of the pool ofmelt pressed up over the outer rim of the head, the space between theend face of the head and the component is reliably and completely filledby the pool of melt which penetrates the carrier, the wall of the recessand the weld-in part and rises adjacently to the wall of the recess, onthe one hand, and passes over the outer rim of the head and the step onthe other hand. This produces mainly an intensive weld in the region ofthe edge of the wall of the recess facing the carrier and the carrierresting on the component and--resembling a riveted joint--thesurrounding of the head in the step region so that the component restingdirectly on the carrier is securely welded at the critical point of theedge of the wall of the recess facing the carrier and, on the otherhand, the weld-in part is continuously drawn to the carrier by the poolof melt passing over the step, the weld-in part pressing the wall partsof the recess connected to it via the pool of melt against the carrier.

Preferably, the weld-in part consists of a shank and a head which isenlarged relative to the shank diameter by a step, protrudes with itsouter rim slightly beyond the component and penetrates into the recessin the component resting on the carrier with a projection such that,owing to the formation of an arc extending to the edge, remote from thecarrier, of the wall of the recess, the projection can be pressed intothe pool of melt to cover the entire wall of the recess including itstwo edges as well as the carrier and the head to its outer rim.

Owing to the construction of the weld-in part from a shank having a headwhich is enlarged relative thereto and which protrudes with its outerrim slightly beyond the component, the effect is achieved that theelectric arc travels from the end face of the head toward this outer rimuntil it reaches the edge, remote from the carrier, of the wall of therecess and incorporates this edge in the pool of melt which is beingformed. The pool of melt is therefore supplied to a considerable extentout of the projection or step of the weld-in part penetrating into therecess of the component so that a pool of melt is formed which coversthe entire wall of the recess including its two edges as well as thecarrier and the head virtually to its outer rim, the step behind theouter rim of the head preventing the electric arc from travelling beyondthe outer rim. Owing to the slight protrusion of the outer rim beyondthe respective edge of the recess, this edge is reliably included in thepool of melt, resulting in reliable welding which covers the entire wallof the recess including its two edges as well as the carrier and thehead up to its outer rim.

The head is preferably constructed such that it is substantiallylenticular in design round its outer rim and the projection projectssubstantially cylindrically round the depth of the recess. Theprojection therefore substantially fills the recess and therefore makesan adequate quantity of material available for the formation of auniform pool of melt on melting.

It is a further object of the invention to design the weld-in part sothat automatic centering of the weld-in part in the recess in the metalcomponent takes place when weld-in part and metal component are broughttogether.

In another preferred embodiment of the invention, this can be achievedin that the rim of the head is designed as a radial melting rim which islocated completely inside the recess in the component and has asubstantially blade-like cross section.

When this weld-in part and the component are brought together, theblade-like rim of the head is received completely within the recess ofthe component, ensuring that the weld-in part does not rest somehowlaterally next to or partially next to the recess of the component.Complete introduction of the rim of the head of the weld-in part intothe recess therefore guarantees centering of weld-in part and recess sothat co-axial centering is not necessary. Even when the rim of theweld-in part does in fact rest on the internal face of the recess,arcing initially occurs at the point of contact when the arc is switchedon and a radial distance is formed between the head and the recess asthe rim melts there so that the arc between the head and the componentis finally distributed over the entire rim of the weld-in part and theentire rim is caused to melt. This produces a distance between the headand the recess which is such that the arc passes over the curvature andconcentrates thereon. This distribution of the arc over the entire rimof the head of the weld-in part causes melting which extends over theentire rim, owing to the blade-like cross section of the rim, andtherefore results in a pool of melt in the region of the bottom of therecess into which the weld-in part can then finally be pressed, asdescribed in the main patent, for welding the component to the carrier.

The blade-like cross section in the region of the rim of the headensures rapid melting of this rim and therefore the direct formation ofthe pool of melt. The blade-like cross section is still maintained inprinciple even if the melting rim is formed as a thin disc projectingradially from the head, as the thin disc projecting radially from thehead, as the thin disc can be melted quickly and the pool of meltconsequently forms correspondingly quickly.

It is yet another object of the invention to design the weld-in part soas to provide substantially uniform heat distribution over the weld-inpart during the welding process. According to the present invention,this may be achieved by providing the weld-in part with a bore whichextends through the shank into the head and is such that the wallthickness of the shank in the bore region corresponds approximately tothe thickness of the end wall of the bore of the welding zone in thewelded state.

The bore extending into the head results, on the one hand, in heatdissipation which is considerably reduced in relation to a solid weld-inpart during the welding process, which has a desirable influence on theenergy requirement for the welding process, and, on the other hand, inheat distribution over all parts to be welded which extendssubstantially uniformly over the parts so that extreme heating atspecific points of the parts to be welded is avoided. The heat capacityof the weld-in part which is reduced owing to the bore extending intothe head also leads to a substantially uniform cooling rate over theentire welding region during the cooling process so that the weld iskept free from internal stresses.

It is expedient to adapt the diameter of the bore to the periphery ofexpanding jaws of a setting tool constructed as a welding tool so thatthe weld-in part can be conveyed in a desirable manner, i.e. it is takenfrom a magazine, transferred to the welding point and positionedthereon. The gripping of the weld-in part via the wall of the boreallows considerable expansion forces and consequently good contact sothat virtually no harmful resistances to transmission can build up atthe contact point. The gripping of the weld-in part from the interiorallows particularly accurate positioning as virtually no displacementthereof can occur when the weld-in part is gripped by the expandingjaws.

The following state of the art is mentioned for the sake ofcompleteness:

A process for fastening plates on aluminium sheets is described in DE-OS3 149 513, in which the plates are provided, in the sense of theabove-mentioned metal component, with a hole to which an aluminium studis inserted as an electrode for an arc welding process. The stud is tobe connected to the metal sheet (in the sense of the foregoing carrier)only but its end face as the plate to be fastened on the the metal sheetis provided, on the side facing the metal sheet, with an indentationwhich receives spurting metal during the welding process and thereforeprevents this metal from passing between plate and metal sheet. Theplate is fastened on the metal sheet by the aluminium stud which ismushroom-shaped and presses onto the plate with its head which isconstructed slightly conically on its underside. The resultant tensileforces are then absorbed only by the welding on the end face of the studas a comprehensive weld which also includes the plate is not intendedwith the process. The idea of including the wall of the recess in theweld, which emerges from the above described invention, and, inparticular, the passing of the melt bath over the step is thereforecompletely lacking in the design produced by the known process.

With a process known from DE 18 11 820 for the welding of studs onto acarrier with interposed zinc-coated sheet metal employing the studwelding process, the hole required in the sheet metal for guidingthrough the stud and welding it to the carrier is provided by burningthrough the sheet metal during the burning of the arc required forwelding. This burning of the arc while the sheet metal is burningthrough is adjusted such that zinc vapours formed in the process areremoved before initiation of the actual welding current for connectingstud and carrier.

Reference is finally made to GB-PS 1 000 577 which disclosed a weld studconsisting of a shank and a head which is enlarged in relation to it andof which the end face forms the weld point. The end face can be conicalor curved in design. In the case of the design with an enlarged head,the curvature passes via a sharp edge in a cone which tapers in thedirection toward the shank and which the cylindrical shank then adjoins.Nothing else about the use of this weld stud can be inferred from thisdocument.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be better understood, a number ofembodiments will be described in greater detail by way of example withreference to the accompanying drawings, in which:

FIG. 1 shows the assembly of carrier, metal component and weld-in partin the position of contact between carrier and weld-in part;

FIG. 2 shows the arrangement of FIG. 1 with the weld-in part lifted fromthe carrier and with the arc formed;

FIG. 3 shows the arrangement of FIG. 1 with a solidified pool of melt;

FIG. 4 is a perspective view of two metal sheets which are welded to oneanother using the embodiment of FIG. 1 and of the weld-in partprojecting from the upper metal sheet;

FIG. 5 shows an alternative weld-in part in a side view;

FIG. 6 shows the weld-in part of FIG. 5 gripped by a setting tool andbrought into the welding position;

FIG. 7 shows the weld-in part of FIG. 5 welded to a carrier and a metalcomponent;

FIG. 8 shows the assembly of carrier, metal component and a modifiedweld-in part in the position of contact between carrier and weld-inpart;

FIG. 9 shows the arrangement of FIG. 8 after electric arc welding with asolidified pool of melt;

FIG. 10 shows a fourth variant of the weld-in part, inserted into ametal component, with lateral contact of the rim of the weld-in part onthe internal face of the recess;

FIG. 11 is a plan view of the weld-in part of FIG. 10;

FIG. 12 shows the weld-in part of FIG. 10 with a firing arc;

FIG. 13 shows a variation of the design of the rim of the weld-in partof FIG. 10 with a sharply issuing edge, and

FIG. 14 shows a further variation of the design of the rim of theweld-in part of FIG. 10.

DETAILED DESCRIPTION OF EMBODIMENTS AND DRAWINGS

Referring to the embodiment illustrated by FIGS. 1, 2, 3 and 4, FIG. 1shows the carrier 1 which is constructed from a piece of sheet metal andonto which the metal component 2, which can be formed, for example, froma sheet metal strip, is placed directly. The metal component 2 isprovided with the recess 3 which is a round bore in the simplest caseinto which the weld-in part or plug 4 is inserted. The weld-in part 4 isheld by a welding tool of which only the holding jaws 5 and 6 areindicated schematically here. As the arc welding process used in thisconnection is a known process, reference is made to known welding toolswhich are provided with corresponding clamping jaws.

The weld-in part 4 has the shank 7 which is preferably cylindrical indesign. The shank 7 passes via the cone 8 into the rim 9 which si alsopreferably constructed cylindrically. The spherically shaped camber 10adjoins the rim 9. Cone 8, rim 9 and camber 10 therefore form a head 11whose external diameter provided by the rim 9 is greater than thediameter of the shank 7. The diameter of the head 11 is smaller than theopening of the recess 3 so that the head 11 is held in the recess 3relative to the component 2 substantially without contact. The cone 8forms the above-mentioned step which can also be constructed as a radialface. A bore 16 which can serve to receive any parts is provided in theshank 7.

The weld-in part 4 is pressed against the carrier 1 by the holding jaws5 and 6. The carrier 1 forms one electrode and the weld-in part 4 theother electrode for a voltage which serves to ignite a welding arc andis applied in a known manner to the welding tool (not shown) and thecarrier 1. The welding arc is then struck in a known manner by liftingthe weld-in part 4 from the carrier 1.

FIG. 2 shows the same arrangement with the struck arc, which isindicated here by the dotted lines 12 radiating from the camber 10.Owing to the contact in the centre of the camber 10 shown in FIG. 1, thewelding arc is initially ignited at this point which, after the weld-inpart 4 has been lifted from the carrier 1, forms the shortest path forthe arc so that the arc causes the carrier to melt in the region of theforemost part of the camber 10 relative to the carrier 1. Owing to thesubsequent increase in the welding current, following in a known manner,the arc also encompasses the outer regions of the camber 10 and finallypasses into the region of the upper edge 13 of the recess 3, producing apool of melt or weld metal which covers the entire surface of thecarrier 1 opposite the camber 10, the camber 10 and the well of therecess 3. A flat cone can also be provided instead of the camber 10.

As the weld-in part 4 is again brought toward the carrier 1, the weld-inpart 4 plunges with its camber 10 in the pool of melt and, in so doing,displaces the melt which, as shown in FIG. 3, rises between the rim 9and the wall of the recess 3 and finally passes over the edge 9 and thecone 8, forming the bead 14. In the process of melting and forming thepool of melt, the edge 15 of the wall of the recess 3 resting on thecarrier 1 is mainly included so that the pool of melt is also formed atthis point which is particularly important for the rigid connection, thepool of melt penetrating into the carrier 1, the component 2 and theweld-in part 4 so as to produce, between the parts, an intimateconnection which is particularly reinforced by the bead 14 which, in amanner of speaking, presses the head 11 of the weld-in part 4 againstthe component as with riveting.

FIG. 4 shows the weld between the carrier 1 and the component 2 in aperspective view. The weld-in part 4 projects from the component 2 roundwhich the bead 14 formed by the raised and solidified pool of meltextends and additionally embraces the weld-in part 4.

The carrier and the metal component may be metal sheets or the like. Itis also possible to construct the metal component as a thickerconstructional element which then merely has to be provided with theabove-described recess into which the head of the weld-in part has topenetrate. The described arc weld is also suitable, in particular, forthe welding of aluminium parts with which welding is known to bedifficult. In particular, aluminium sheets can only be connected to oneanother with difficulty by the known spot welding process as the oxideskin present on the aluminium sheets has to be broken through. Apartfrom this, it should be noted during spot welding that the electrodesplaced on the metal sheets are contaminated relatively rapidly andtherefore have to be continually cleaned. With the arc welded jointaccording to the invention, on the other hand, new electrodes areconstantly provided, namely in the form of the carrier on the one handand in the form of the weld-in part on the other hand.

Referring to the embodiment illustrated by FIGS. 8 and 9, FIG. 8 showsthe carrier 1 which is formed from a piece of sheet metal and onto whichthere is directly placed the metal component 2 which can be formed, forexample, from a sheet metal strip. The metal component 2 is providedwith the recess 3, a round bore into which the weld-in part 4 isinserted in the simplest case. The weld-in part 4 is held in a knownmanner by any welding tool.

The weld-in part 4 has the shank 7 which is preferably cylindrical inconstruction. The shank 7 passes into the lenticular head 11 whichextends via the conical step 8 to its outer rim 9. The outer rim 9protrudes slightly beyond the component 2, i.e. the rim 9 has a slightlygreater diameter than the recess 3 in the case of cylindrical design.The lenticular head 11 is then followed by the step 17 which penetratesinto the recess 3 and finally passes into the cone 10 resting with itstip 18 on the carrier 1. The weld-in part 4 and the carrier 1 form thetwo electrodes for the electric arc which is being formed, an electriccontact between the carrier 1 and the metal component 2 obviously alsoexisting owing to the resting of the metal component 2 on the carrier 1.

The step 17 has a somewhat smaller diameter than the recess 3 so that,after retraction of the weld-in part 4 from the carrier 1, an electricarc is formed between the cone 10 and the carrier 1, the electric arcexpanding with a corresponding increase in the welding current over thetotal projection 3 and the head 11 to the outer rim 9 thereof. Theelectric arc causes the edge 13 to melt in the region between the outerrim 9 and the edge 13 of the component 2. The pool of melt being formedbetween the cone 10 and the carrier 1 is also supplied by material fromthe step 17 so that the pressing of the weld-in part 4 into the pool ofmelt results in welding to beyond the edge 13 which is partially meltedin the process, forming an intimate rigid joint between the weld-in part4, the component 2 and the carrier 1.

FIG. 9 shows the welded-in weld-in part 4. As shown, a weld zone 19which extends to and includes the outer rim 9 is formed. The moltenouter rim 9 is located substantially at the level of the surface, remotefrom the carrier 1, of the component 2, the weld-in zone 19 being shownas a slight elevation at the surface of the component.

Referring now to the embodiment illustrated in FIGS. 10, 11, 12 and 13,FIG. 10 shows the carrier 1 which is formed from a piece of sheet metaland onto which the metal component 2, which may be formed, for example,by a strip of sheet metal, is placed directly. The metal component 2 isprovided with the recess 3, in the simplest case a round bore into whichthe weld-in part 4 is inserted. As described above, the weld-in part 4is held by a suitable welding tool and is introduced into the recess 3.

The weld-in part 4 has the stem 7 which is preferably cylindrical indesign. The head 11 is formed from the cone 8, the thin disc 9A and thecamber 10 adjoins the stem 7. In this case, the thin disc 9A projectsradially outwardly in the form of a blade or disc from the head 11. Thediameter of the thin disc 9A is smaller than the diameter of the recess3 so that the thin disc 9A rests completely within the recess 3 whenweld-in part 4 and component 2 are brought together. The height of thecamber 10 and the thickness of the component 2 are appropriately adaptedto one another.

The weld-in part 4 is automatically centred relative to the component 2as weld-in part 4 and component 2 are brought together because the thindisc 9A has a smaller diameter than the recess 3, and it is quitepossible for the thin disc 9A to come into contact with the wall of therecess 3, as shown at point 12.

FIG. 11 shows the weld-in part 4 according to FIG. 10 together with thecomponent 2, more specifically as viewed from the side of the camber 10.FIG. 11 shows the projection of the thin disc 9A, extending beyond theedge 13, relative to the camber 10. FIG. 11 also shows the distance Dfrom the contact point 12. In this position of weld-in part 4 relativeto component 2, the distance D corresponds to about twice the differencein the diameters of weld-in part 4 and recess 3.

FIG. 12 shows how the melting process initially takes place in theregion of the contact point 12 (see FIG. 10) after the arc has beenswitched on (represented by the radiating lines 14). The thin disc 9A isreduced here by melting until it passes into the region of the cone 8and the camber 10, and as the distance between the remainder of the thindisc 9A and the internal wall of the recess 3 increases, the arc isdistributed, in particular over the camber 10, which therefore melts andleads to a molten pool on the bottom of the component 2 on the surfaceof the carrier 1, into which pool the weld-in part 4 is finallyimmersed, the molten pool extending over the entire camber 10, theopposing region of the carrier 1 and the internal wall of the recess 3.A secure weld between component 2 and carrier 1 is finally produced inthis way by the molten material which has melted from the thin disc 9A.

FIG. 13 shows a detail of a variation of the design of the weld-in part.In this case, the weld-in part 4 passes via the cone 11 into a sharplyissuing cutting edge 15, the camber 10 facing the cone 11 on the otherside of the cutting edge 15. The cutting edge 15 projecting similarly tothe thin disc 9A of FIG. 10 ensures that rapid melting of the materialof the weld-in part 4 can take place in the region thereof. The actionof the weld-in part 4 shown in FIG. 13 is basically the same as that ofthe weld-in part 4 according to FIG. 10.

A further design of the weld-in part 4 is shown in FIG. 14. In this casethe cone 8 of the weld-in part 4 runs onto a radial face 16 which islimited outwardly by the edge 17 from which the camber 10 extends.Depending on the height of the camber 10, a more or less thin cuttingedge-like rim with the relatively sharp edge 17 is therefore formed andcan be caused to melt in the manner described with reference to theaforementioned embodiments.

Referring to the embodiment illustrated by FIGS. 5, 6 and 7, the weld-inpart 4 shown in FIG. 5 has shank 7 which is cylindrical in design. Theshank 7 passes via the cone 8 into the rim 9 which is also generallycylindrical in shape. The convexly shaped camber 10 adjoins the rim 9.Cone 8, rim 9 and camber 10 therefore form a head 11 of which theexternal diameter produced by the rim 9 is greater than the diameter ofthe shank 7. The diameter of the head 11 is smaller than the opening ofthe recess 3 shown in FIG. 6. The cone 8 forms a step which can also beconstructed as a radial face. The bore 16 is provided in the weld-inpart through shank 7 and extends into the head 11. The end wall 17A ofthe bore 16 has a thickness corresponding approximately to the thicknessof the wall 18 of the shank 7.

FIG. 6 shows the weld-in part 4 according to FIG. 5 in section, morespecifically inserted into the recess 3 in the metal component 2. In thesimplest case, the recess 3 consists of a round bore. The metalcomponent 2 lies directly on the carrier 1 consisting of a piece ofsheet metal. The metal component 2 is additionally pressed against thecarrier 1 by the two pressing members 19, 20.

According to FIG. 6, the conveyance and positioning of the weld-in part4 is brought about by the setting tool 21 which engages bore 16 with itsexpanding jaws 22, 23 during the expansion of which the weld-in part 4is kept tensioned from the interior. The expanding jaws are expanded bymeans of the expansion mandrel 24 which, as with known expansion tools,urges the expanding jaws 22 and 23 outwardly when driven in between theexpanding jaws 22 and 23. The setting tool 21 has a total of foursymmetrically-arranged expanding jaws, of which the illustratedexpanding jaws 22, 23 are separated from one another by the slot 25. Thesetting tool 21 is designed as a welding tool, i.e. it is attached to apole of a voltage source for arc welding. The other pole is connected tothe carrier 1. The weld-in .part 4 and the carrier 1 therefore form thetwo electrodes for arc welding, good contact with the weld-in part 4being produced owing to the easily produced considerable expanding forceof the expanding jaws 22, 23.

The weld-in part 4 is pressed against the carrier 1 by the setting tool21, the voltage source for arc welding being attached to the weld-inpart 4 and the carrier 1, as mentioned above. The welding arc is thenstruck in a known manner, for which purpose the setting tool 21 islifted from the carrier 1 together with the weld-in part 4.

An arc is therefore struck between carrier 1 and the weld-in part 4,leading to the formation of a pool of melt and eventually to the weldingof the respective parts, as already described hereinbefore.

The final welded joint is shown in a perspective view in FIG. 7. Itshows the carrier 1 with the component 2 from which the weld-in part 4projects. A bead 14 formed by the raised pool of melt extends around theweld-in part 4, additionally embracing the weld-in part 4.

Owing to the bore 16 extending into the head 11, the weld-in part 4forms a hollow body with a wall having substantially the same thickness,in particular in the region of the wall of the bore 16 and the end wall17A thereof. As a result, the weld-in part has a relatively low heatcapacity, that is to say can be heated suitably rapidly. During thecooling of the weld-in part 4, this process also takes place without aparticularly high heat concentration as individual points of the weld-inpart, producing a substantially tension-free welding zone after coolinghas taken place.

The carrier and the metal component can be metal sheets or the like. Itis also possible to design the metal component as a strongerconstructional element which then merely has to be provided with theabove described recess into which the head of the weld-in part has topenetrate. The described arc welded joint is suitable, in particular,also for the welding of aluminium parts with which welding is known tobe difficult. In particular, aluminium sheets can be joined to oneanother only with difficulty by the known spot welding process as theoxide skin present on the aluminium sheets has to be broken through. Inaddition, it should be noted during spot welding that the electrodesplaced onto the metal sheets are contaminated relatively rapidly andtherefore have to be cleaned continually. With the arc welded jointaccording to the invention, on the other hand, new electrodes arepresent continuously, namely in the form of the carrier on the one handand in the form of the weld-in part on the other hand. As particularlyhigh currents are required when welding aluminium, the contact of theweld-in part via the internal wall of its bore with the easily appliedhigh contact pressures has a particularly desirable effect.

We claim:
 1. A welded joint comprisinga sheet-like metal carrier; asheet-like metal component overlying said carrier, said component havinga bore therethrough; a plug comprising a shank; and an enlarged head onone end of said shank, at least a portion of said head being locatedwithin said bore; said head having a surface surrounding said shank andfacing away from said carrier; and a solidified body of weld metal insaid bore, said body comprising metal from said carrier, said componentand said plug, said body being fused to and joining said carrier, saidcomponent and said plug; said body further extending beyond the surfaceof said head on the side opposite said carrier to increase the strengthof said joint.
 2. A welded joint as claimed in claim 1 wherein said bodyoverlies part of said surface of said head.
 3. A welded joint as claimedin claim 1 wherein said shank protrudes above said head sufficiently tobe engaged by a welding tool.
 4. A welded joint as claimed in claim 1wherein said plug is provided with an axial bore extending through saidshank into said head.
 5. A welded joint as claimed in claim 4 wherein awall thickness of said shank around said axial bore is substantiallyequal to a thickness of an unmelted portion of said head at the end ofsaid axial bore.
 6. A welded joint as claimed in claim 1 wherein saidshank extends outwardly from said joint in a position to receivefastening elements thereon.
 7. A welded joint according to claim 1wherein the upper surface of said head is tapered conically toward saidshank.
 8. A welded joint as claimed in claim 1 wherein said bodyincludes metal from an entire surface of said bore in said component. 9.A welded joint as claimed in claim 1 wherein said body overlies part ofsaid surface of said head.